It is known to use a drying device designed as a drying tunnel for such drying. With such a drying device, the bulk material is transported on a surface in a horizontal direction and surrounded by an airflow that draws moisture from the bulk material. The surface on which the bulk material is transported, can, for example, be a conveyor belt, or can be formed by several plates that adjoin each other and are arranged adjacent to one another thus forming a conveying surface. The conveyor belt and the plates can be perforated with holes, slots or other openings to allow the air flow to better access the bulk material and to flow through the bulk material. This can help to accelerate the drying with certain types of bulk material.
These types of drying devices are typically operated in a continuous process. The moist bulk material is thereby deposited on the plates at a loading site, the plates are continuously moved on an enclosed rail within the drying device, and the dried bulk material is removed from this rail at an extraction site, preferably by tipping the plates in conjunction with the respective effect of gravity on the bulk material. It is known to design drying devices in a way that they comprise two or more drying levels. The bulk material is typically led to the first upper level, transported on this level through a drying tunnel, whereby moisture is drawn from the bulk material during this transportation, and finally delivered by gravitational force at an end of the drying tunnel to a lower level. The bulk material is again led through the drying tunnel on said lower level, whereby the conveying direction is opposed to the preceding conveying direction on the upper level, and more moisture is drawn from the bulk material. After passing through the drying tunnel on the lower level, the bulk material can be loaded to a further, deeper third level, and once again pass through the drying tunnel on this third level for moisture withdrawal. In this manner, according to the type of drying tunnel, two, three, four or even more levels, preferably an even number of levels, can be provided, on which the bulk material passes through the drying tunnel in a reciprocating transport movement, thereby increasingly losing moisture, so as to be then loaded from the lowest level into a collection point, from which the dried bulk material is removed by appropriate means, for example an auger, and used for backfill or other further processing.
It is generally known to provide the several levels on which the bulk material is transported in one single continuous conveyor belt, which is accordingly deflected in deflecting devices at the end. Alternatively, it is also known to provide the several levels by means of respectively several separate continuous transportation devices, which, for example, consist of an upper and a lower run and are each deflected at the end by 180°.
With said drying devices that are known, for example, from EP2003412A1 according to the design of a drying tunnel, efficient drying of bulk material is achieved in many applications. The drying performance can be set by adjusting the length of the drying tunnel, the number of drying levels, and the volume of the air flow rate of the drying air, as well as the temperature and the humidity of this drying air, so as to achieve a high drying performance. However, there is a demand for drying devices that are able to dry moist bulk material in an economically more efficient manner than known drying devices.
Said demand according to the invention is fulfilled by proposing a drying device with the design described above, in which a scraper device is arranged in the area of the first or second deflection rail section, which comprises one or more scraping elements that are arranged in such a way that the location surface of a perforated plate moving along the first or second deflection rail section comes into contact with the scraping elements and is cleaned by means of a relative movement between the scraping elements and the perforated plate.
The invention is based on the findings that an increase in the efficiency of the drying effect can be achieved with unchanged use of energy and dimensions of the drying device if the location surfaces of the plates of a drying device, on which the bulk material is transported within the drying device, can be effectively cleaned after passing through an upper rail section by providing one or several scraping elements, which perform a relative movement to the plates. Said relative movement can in particular be provided by guiding the plates along the scraping elements, preferably on the path of these plates along the deflection rail section. The cleaning of the location surface obtained in this way ensures that bulk material parts sticking to the location surface are effectively removed, thus preventing the formation of a layer on this location surface. In this way, the bulk material that reaches the location surface can always come into direct contact with the plate, and the heat conduction from the plate to the bulk material can be constantly maintained at a high level, which further increases the drying effect. In addition, if perforated plates are being used, bulk material which has accumulated in the openings in the plates, i.e. the perforations, can be removed by means of the relative movement between the scraping elements and the bulk material of the plates, thus preventing blockage of these openings. In this way, an airflow passing through the perforations that is beneficial to an effective and efficient drying can be maintained and ensured during operation for practically all perforations, which increases the drying efficiency.
The invention has the special feature that the scraper device is arranged in the deflection rail section, which achieves the advantage that the plates can be cleaned with the scraper device if there is no bulk material on them. This feature is provided according to the invention, although the plates do not typically move in the deflection rail section in a horizontal movement path, but are instead deflected, and can therefore not be easily cleaned in a process that requires mechanical contact.